1. Field of the Invention
The present invention relates to a polishing machine and a polishing method of polishing work pieces such as semiconductor device wafers, or optical parts, functional parts, mechanical parts, etc. that require parallelism and flatness, and particularly to enhancement of the parallelism and flatness of the work piece realized by simultaneously polishing both front and back surfaces of each work piece, and miniaturization of the machine.
2. Discussion of the Background
As a polishing machine which polishes both surfaces of a disc-like work piece such as a semiconductor device wafer, a batch-type polishing machine 10 for loading a plurality of wafers W at one time as shown in FIG. 4 is well known. In the polishing machine 10, an upper surface plate 11 and a lower surface plate 12 are provided to face one another and a plurality of wafers W supported by internal gears 13 are loaded between the upper surface plate 11 and the lower surface plate 12. The internal gears 13 revolves while rotating around a sun gear 14 provided at the center of the machine. With this structure, both surfaces of each wafer W are uniformly polished by polishing cloths 11a and 12a provided respectively on the upper surface plate 11 and the lower surface plate 12.
The above-described conventional batch-type polishing machine 10 has the following problem. A plurality of wafers W are processed simultaneously, and S if the thicknesses of the wafers W before polished are not uniform, the upper surface plate 11 or the lower surface plate 12 is inclined, which causes poor accuracy in the parallelism or flatness after the polishing.
Further, it is difficult to uniformly adjust the thicknesses of large wafers W such as Si wafers whose diameter ranges 8 to 12 inches, before polishing.
On the other hand, as such a polishing machine 10 is structurally in a large scale, the upper surface plate 11 and the lower surface plate 12 are larger as the wafers W are larger, which makes high accuracy flattening and management of the surface plates that influence the accuracy in polishing difficult. At the same time, the required installation area of the polishing machine 10 is increased, and installing it in a limited space such as a clean room and the like is limited.